The purpose of gait analysis is to qualify a person's walking pattern and the neuromuscular strategies used by the body to produce the observed movement. A computerized video camera system measures the movement pattern and special platforms built into the floor measure forces acting on the feet. From the measured movements and forces, the mechanical work done by the body during walking can be estimated. Current techniques used to approximate work oversimplify the model of the body and its movements and introduce errors into the estimates. The purpose of our research is to investigate more complex models of the body to learn how these models affect mechanical work estimates. One study of 20 normal subjects that examined the work done at the ankle joint during gait has been accepted for publication. The study employed a more sophisticated model of the ankle joint and included additional terms, previously ignored, in the mechanical work calculations. Another study currently underway will examine the work done at the knee joint of the same ten subjects. Finally, a third study of another 15 subjects suggests the model of the foot and the assumptions made about its behavior during gait result in erroneous estimates of work done by the foot. The results of these studies strongly suggest that these new approaches are essential to improving the validity of mechanical work estimates. The use of these estimates in gait analysis will have implications for rehabilitation and surgical treatment planning in patient populations.